Buoyant instabilities in downward flow in a symmetrically heated vertical channel

Technical Report · Mon Jul 01 04:00:00 EDT 1996

DOI:https://doi.org/10.2172/417001· OSTI ID:417001

Evans, G ^[1]; Greif, R ^[2]

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1. Sandia National Lab., Livermore, CA (United States)
2. Univ. of California, Berkeley, CA (United States)

This study of the downward flow of nitrogen in a tall, partially heated vertical channel (upstream isothermal at T{sub in}*, heated region isothermal at T{sub s}* downstream adiabatic) shows the strong effects of buoyancy even for small temperature differences. Time-dependent oscillations including periodic flow reversals occur along the channel walls. Although the flow and heat transfer are asymmetric, the temperature and axial component of velocity show symmetric reflections at two times that are half a period apart and the lateral component of velocity shows antisymmetric reflections at the two times. There is strong interaction between the downward flow in the central region of the channel and the upward flow along the heated channel walls. At the top of the heated region, the upward buoyant flow turns toward the center of the channel and is incorporated into the downward flow. Along the channel centerline there are nonmonotonic variations of the axial component of velocity and temperature and a large lateral component of velocity that reverses direction periodically. Results are presented for Re = 219.7 and Gr/Re{sup 2} = 1.83, 8.0, and 13.7. The heat transfer and the frequency of the oscillations increases and the flow and temperature fields become more complex as Gr/Re{sup 2} increases. The results have applications to fiber drying, food processing, crystal growth, solar energy collection, cooling of electronic circuits, ventilation, etc.

• Research Organization: Sandia Labs., Livermore, CA (United States)
• Sponsoring Organization: USDOE Office of Energy Research, Washington, DC (United States); Department of Defense, Washington, DC (United States)
• DOE Contract Number: AC04-94AL85000
• OSTI ID: 417001
• Report Number(s): SAND--96-8250; ON: DE97050547; CNN: Order No. 8951DPAM21264
• Country of Publication: United States
• Language: English

Related Subjects

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION
42 ENGINEERING
COOLING
DRYING
ELECTRONIC CIRCUITS
FOOD PROCESSING
GAS FLOW
HEAT TRANSFER
HEATING
MATHEMATICAL MODELS
NITROGEN
OSCILLATIONS
TEMPERATURE DEPENDENCE
VELOCITY